A number of seating devices have been previously proposed for improving comfort and blood circulation in the lower part of the body. For example, U.S. Pat. No. 2,684,672 describes a body support device in the form of a seat that can be used by pilots. It includes a flexible cushion divided into airtight chambers which rise or fall when air is fed under the influence of a control apparatus to alternate sets of chambers. The inflatable cushion is, however, subject to being punctured but more importantly it has a tendency to trap body moisture between itself and the skin of the person using it because it must be air impermeable. By contrast, U.S. Pat. Nos. 3,970,077, 2,445,158 and 2,773,498 show various forms of beds or chairs with movable support surfaces that are raised and lowered during operation by means of cams mounted on rotating shafts which during operation contact suitable cam followers to lift one, two or three sets of supporting blocks into contact with the skin to thereby provide support for the body at different locations depending upon whether the blocks are raised or lowered. These devices have significant shortcomings. First, the motor used for raising or lowering the suppporting blocks must, of necessity, be mounted on the seat itself making the seat heavy and bulky. In addition, the cam mechanism adds further to its cost and can become worn or out of adjustment. In addition, the seat can become noisy to operate if the parts begin to wear where the cam followers rub against the cam surfaces. The result is an expensive, cumbersome and complicated mechanism which is subject to wear and there is a considerable opportunity for the device to malfunction.
The present seat has several benefits. First, it is very comfortable for such as heavy equipment operators and airplane pilots who are required to remain seated for long periods of time. Another benefit of the invention is in the promotion of better blood circulation. This helps to alleviate the formation of what are commonly referred to as pressure sores or decubitus ulcers. Although decubitus ulcer development can be resisted by maintaining good nutrition and hygiene, it still occurs, for example, among wheelchair-bound persons who experience prolonged local body pressure against the seat in excess of 25 mm Hg(which is equivalent to 0.5 lb. per square inch or 13.4 inches of water). This static pressure is generally considered enough to compress the capillaries and shut off circulation to the skin and underlying tissues. Tissue death then proceeds unless the body is moved to bring other tissues into a weight supporting role and the closed capillaries are allowed to reopen and resupply the denied tissues. Normally, body movement enables muscles and tissues to avoid deterioration resulting from immobility, but persons with spinal cord injury or muscular debility may not be able to reposition their weight or even sense the discomfort of their support areas, which increases the risk that they will develop pressure sores. Moreover, the maceration damage to the skin of incontinent patient's and the maintenance of good skin hygiene is affected by the ability of the patient's supporting seat or couch to carry away water from the skin and allow air circulation over the skin. There is often not enough time for unhurried and careful massage of delicate tissues by nurses whose work schedules are full. It would be beneficial if the patient's supporting seat, whether or not a part of a wheelchair, could provide an action adapted to shift support points from time to time. Nurses must also have good control over a patient in order not to bruise or shear damage the patient's skin or strain themselves. In general, nurses favor systems which do not complicate or slow their work. The patient care institution shares these preferences for a support seat that increases patient benefits and does these things reliably and with cost effectiveness.
Alternating pressure pad (A.P.P.) systems in common use for the treatment of patients suffering from pressure sores consist of a series of intermingled, variously shaped, inflatable tubes upon which the patient lies or sits. During use, alternate sets of tubes are inflated and deflated repeatedly thereby shifting the support points. These devices are helpful but, like the pilot's seat described above, they are subject to puncture and tend to trap moisture between the patient's skin and the air impermeable air inflated tubes.
When used as seat cushions, inflatable tubes constitute an unstable shifting support which complicates posture control. Additionally, because of their power requirements, A.P.P. wheelchair cushions have not been marketed as battery powered devices, but have been powered from 117 volt Ac wall outlets.
The general objective of the present invention is to overcome these and other deficiencies of the prior art and to provide an improved seat having a multiplicity of supporting surfaces adapted to alternately and selectively support different areas of the body to thereby shift the points of support from time to time while eliminating mechanical mechanisms employed for moving the support surfaces into and out of engagement with the body of the user. These and other more detailed and specific objects will be apparent by reference to the following specification and figures.